Re: EOL conversion of files in .tar archives

From:

Eli Zaretskii

Subject:

Re: EOL conversion of files in .tar archives

Date:

Tue, 22 May 2007 14:19:14 +0300

> From: Kenichi Handa <address@hidden>
> CC: address@hidden
> Date: Mon, 21 May 2007 13:48:20 +0900
>
> In article <address@hidden>, Eli Zaretskii <address@hidden> writes:
>
> > Lately I noticed that, in the Windows port of Emacs, visiting files in
> > .tar archives shows them as if they had DOS EOLs, even though the
> > files have Unix EOLs. (This is not due to some recent change: it
> > looks like Emacs behaved like that since before the pretest.)
>
> > Is this intentional, or should I debug it? If the former, can someone
> > explain the rationale?
>
> I think it is a bug of find-buffer-file-type-coding-system
> (dos-w32.el). If TARGET is (FILENAME . BUFFER), it should
> assume that the file contents is available. Could you
> verify that the attached patch is correct?
I'm uneasy about patching find-buffer-file-type-coding-system at this
stage, since it is so widely used. For example,
decode-coding-inserted-region also invokes
find-operation-coding-system with second argument a cons cell, and it
is not clear to me that your change will DTRT in that case.
I'd like to suggest an alternative change that is local to
tar-mode.el, see below. It mimics what arc-mode.el does.
This solves the problem with the EOL decoding, but reveals a very
strange phenomenon: dos-w32.el and dos-w32.elc behave differently.
The latter is preloaded into Emacs on Windows, and if I visit a file
inside a tarball (after applying the patch below), plain text files
with Unix EOLs get latin-1-unix buffer-file-coding-system, instead of
the expected undecided-unix. But if I manually load dos-w32.el and
visit the same file again, its buffer-file-coding-system is now
undecided-unix, as expected! Is this some problem with the byte
compiler?
Index: lisp/tar-mode.el
===================================================================
RCS file: /cvsroot/emacs/emacs/lisp/tar-mode.el,v
retrieving revision 1.108
diff -u -r1.108 tar-mode.el
--- lisp/tar-mode.el 21 Jan 2007 03:53:10 -0000 1.108
+++ lisp/tar-mode.el 22 May 2007 11:18:19 -0000
@@ -681,6 +681,12 @@
(goto-char (posn-point (event-end event)))
(tar-extract))
+(defun tar-file-name-handler (op &rest args)
+ "Helper function for `tar-extract'."
+ (or (eq op 'file-exists-p)
+ (let ((file-name-handler-alist nil))
+ (apply op args))))
+
(defun tar-extract (&optional other-window-p)
"In Tar mode, extract this entry of the tar file into its own buffer."
(interactive)
@@ -735,9 +741,17 @@
(save-excursion
(funcall set-auto-coding-function
name (- (point-max) (point)))))
- (car (find-operation-coding-system
- 'insert-file-contents
- (cons name (current-buffer)) t))))
+ ;; The following binding causes
+ ;; find-buffer-file-type-coding-system
+ ;; (defined on dos-w32.el) to act as if
+ ;; the file being extracted existed, so
+ ;; that the file's contents' encoding is
+ ;; auto-detected.
+ (let ((file-name-handler-alist
+ '(("" . tar-file-name-handler))))
+ (car (find-operation-coding-system
+ 'insert-file-contents
+ (cons name (current-buffer)) t)))))
(multibyte enable-multibyte-characters)
(detected (detect-coding-region
(point-min)